Sheet-like article and a production method therefor

ABSTRACT

The invention relates to an environmentally friendly production method for a sheet-like article that does not use an organic solvent in the production process and provides a sheet-like article that compares favorably in terms of a uniform feel with artificial leather products produced from an organic solvent based polyurethane and in particular has good surface quality and texture and also provides a production method therefor. The present invention aims to provide a sheet-like article comprising a fibrous base material formed of ultrafine fibers and/or ultrafine fiber bundles provided with, as a binder, a polymer elastomer having a hydrophilic group, any thickness-directional cross section of the sheet-like article containing regions occupied by the polymer elastomer, the regions including independent regions each with a cross-sectional area of 50 μm2 or more, the total area of the independent regions accounting for 0.1% or more and 5.0% or less of the cross-sectional area of the artificial leather in an observation view field. The production method for the sheet-like article according to the present invention provides a production process for a sheet-like article including a fibrous base material formed of ultrafine fibers and, as a binder, a polymer elastomer having a hydrophilic group, the process including a step for adding an aqueous resin dispersion liquid containing a water-dispersed polymer elastomer and a viscosity improver to a fibrous base material and a step for coagulating the polymer elastomer in hot water at a temperature of 50° C. to 100° C.

CROSS-REFERENCE TO RELATED APPLICATIONS

This is a divisional patent application of U.S. National PhaseApplication 15/119,025, filed on Aug. 15, 2016, which is a U.S. NationalPhase application of PCT/JP2015/054941, filed on Feb. 23, 2015, andclaims priority to Japanese Patent Application No. 2014-036516, filed onFeb. 27, 2014, the disclosures of each of these applications beingincorporated herein by reference in their entireties for all purposes.

FIELD OF THE INVENTION

The invention relates to an environmentally friendly production methodfor a sheet-like article that does not use an organic solvent in theproduction process and particularly relates to a sheet-like article thathas good surface quality and texture and to a production methodtherefor.

BACKGROUND OF THE INVENTION

Sheet-like articles made up mainly of a fibrous base material, such asnonwoven fabric, and polyurethane have excellent features that naturalleathers do not have, and are widely utilized in various uses such asartificial leather. In particular, a sheet-like article that employs apolyester-based fibrous base material is excellent in light resistance,and therefore its use has spread year by year to products such asclothing, chair upholstery, automotive interior finishing material uses,etc.

To produce such a sheet-like article, a generally adopted method is acombination of processes in which a fibrous base material is impregnatedwith an organic solvent solution of polyurethane and then the fibrousbase material obtained is immersed in water or an aqueous solution of anorganic solvent that is a non-dissolving medium for polyurethane, so asto cause polyurethane to undergo wet coagulation. Here, examples of theorganic solvent for polyurethane include water-miscible solvents such asN,N-dimethyl formaldehyde. However, since organic solvents are generallyhigh in harmfulness to the human body and the environment, theproduction of a sheet-like article strongly requires a technique thatdoes not use an organic solvent.

Specific proposed solutions to this problem include the adoption ofwater-dispersed polyurethane, which is prepared by adding a hydrophilicgroup into the molecular chain of polyurethane and dispersing thepolyurethane resin in water, instead of the conventional method of usingorganic solvent based polyurethane.

However, sheet-like articles that are produced by impregnating a fibrousbase material with a dispersion liquid of a water-dispersiblepolyurethane, which is prepared by dispersing a water-dispersiblepolyurethane in a liquid, and subsequently coagulating the polyurethanetend to have the problem of stiff texture.

One of the major reasons is the difference between them in terms of thecoagulation technique used. Specifically, the method involving thecoagulation of a polyurethane solution in an organic solvent uses theso-called wet coagulation technique in which polyurethane moleculesdissolved in an organic solvent are coagulated by substituting water forsolvent. When applied to polyurethane, the technique produceslow-density, porous film. Accordingly, if polyurethane is coagulatedafter penetrating into the fibrous base material, the contact areabetween the fiber and polyurethane decreases, leading to a softsheet-like article.

For coagulation of water-dispersed polyurethane, on the other hand, thewet heat coagulation technique is mainly used, in which heating isperformed to destroy the hydrated state of the dispersion liquid ofwater-dispersed polyurethane to cause the aggregation of emulsionparticles of polyurethane to achieve coagulation. The resultingpolyurethane film has a high-density, nonporous film structure.Consequently, strong contact is developed between the fibrous basematerial and polyurethane to maintain strong entanglement of fibers,leading to stiff texture.

To improve the texture attributed to the use of water-dispersedpolyurethane, that is, to prevent the polyurethane from holding thefiber entanglement, a technique has been proposed which allows thepolyurethane in the fibrous base material to have a porous structure.

Specifically, there is a proposed method in which the structure ofpolyurethane in a fibrous base material, such as nonwoven fabric, ismade porous by adding to the fiber base material a water-dispersedpolyurethane liquid that contains a foaming agent and causing thefoaming agent to foam by heating (refer to Patent document 1). In thisproposal, water-dispersed polyurethane is made porous so that thecontact area between the fiber and the polyurethane decreases to weakenthe force to hold fiber entanglement, thereby providing a sheet-likearticle having a good texture with soft feel. However, such texturestill tends to be poor in softness compared to products produced from abase material containing a solution of polyurethane in an organicsolvent.

To develop a porous polyurethane structure in a fibrous base material,there is another proposed technique in which a dispersion liquid ofwater-dispersed polyurethane containing an association type viscosityimprover is added to a fibrous base material, which is then subjected towet-heat coagulation, thereby producing a porous structure fromwater-dispersed polyurethane (see Patent document 2). In this proposal,too, water-dispersed polyurethane is made porous so that the contactarea between the fiber and the polyurethane decreases to weaken theforce to hold fiber entanglement, thereby providing a sheet-like articlehaving a good texture with soft feel. However, such texture still tendsto be poor in softness compared to products produced from a basematerial containing a solution of polyurethane in an organic solvent.

PATENT DOCUMENTS

[Patent document 1] Japanese Unexamined Patent Publication (Kokai) No.2011-214210

[Patent document 2] Japanese Patent No. 4042016

SUMMARY OF THE INVENTION

An object of the present invention is to provide a sheet-like articlethat can be produced from an environment-friendly production process,compares favorably in terms of a uniform feel with artificial leatherproducts produced from organic solvent based polyurethane, and haselegant surface quality and good texture, and also relates to aproduction method therefor.

Another object of the present invention is to provide a sheet-likearticle that contains a porous polyurethane structure produced fromwater-dispersed polyurethane and has fold and crease recoverability andflexibility equivalent to those of artificial leather products producedfrom solvent based polyurethane, and also relates to a production methodtherefor.

The present invention aims to meet the above objectives and thesheet-like article according to embodiments of the invention includes afibrous base material formed of ultrafine fibers and/or ultrafine fiberbundles that contains, as a binder, a polymer elastomer having ahydrophilic group, any thickness-directional cross section of thesheet-like article containing regions occupied by the polymer elastomer,the regions including independent regions each with a cross-sectionalarea of 50 μm² or more, the total area of the independent regionsaccounting for 0.1% or more and 5.0% or less of the cross-sectional areaof the artificial leather in an observation view field.

In a preferred embodiment of the sheet-like article according to thepresent invention, 1% or more and 35% or less of the circumferences ofthe cross sections of the ultrafine fibers and/or ultrafine fiberbundles observed in a cross section made by cutting the sheet-likearticle in the thickness direction are covered by film of the polymerelastomer.

Another preferred embodiment of the sheet-like article according to thepresent invention is a sheet-like article as described in either claim 1or 2, wherein the polymer elastomer has a crosslinked structure formedby using a crosslinking agent.

The present invention aims to meet the above objectives and theproduction method for the sheet-like article according to embodiments ofthe present invention provides a production process for a sheet-likearticle including a fibrous base material formed of ultrafine fibersand, as a binder, a polymer elastomer having a hydrophilic group, theprocess including a step for adding an aqueous resin dispersion liquidcontaining a water-dispersed polymer elastomer and a viscosity improverto a fibrous base material and a step for coagulating the polymerelastomer in hot water at a temperature of 50° C. to 100° C.

In a preferred embodiment of the production method for the sheet-likearticle according to the present invention, the aqueous resin dispersionliquid shows non-Newtonian characteristics.

In a preferred embodiment of the production method for the sheet-likearticle according to the present invention, the viscosity improver is anonionic type viscosity improver.

In a preferred embodiment of the production method for the sheet-likearticle according to the present invention, the aqueous resin dispersionliquid shows thixotropy.

In a preferred embodiment of the production method for the sheet-likearticle according to the present invention, the viscosity improvercontained in the aqueous resin dispersion liquid is a polysaccharideviscosity improver.

In a preferred embodiment of the production method for the sheet-likearticle according to the present invention, the viscosity improver isguar gum.

In a preferred embodiment of the production method for the sheet-likearticle according to the present invention, the aqueous resin dispersionliquid contains a thermosensitive coagulant.

In a preferred embodiment of the production method for the sheet-likearticle according to the present invention, the aqueous resin dispersionliquid contains a crosslinking agent.

According to the present invention, a porous structure can be developedfrom water-dispersed polyurethane using an environment-friendlyproduction process to achieve fold and crease recoverability andflexibility closely equivalent to those of products produced from afibrous base material containing organic solvent based polyurethane,making it possible to provide a sheet-like article containing raisedhairs with a uniform length similar to those in artificial leatherproduced from organic solvent based polyurethane and having elegantsurface quality with a dense fiber feel and good texture with highflexibility and crease recoverability.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a SEM photograph given as a substitute for a drawing of across section of the artificial leather prepared in Example 13.

FIG. 2 is a SEM photograph given as a substitute for a drawing of across section of the artificial leather prepared in Comparative example4.

FIG. 3 is a SEM photograph given as a substitute for a drawing forshowing an outline of the method for calculating the proportionaccounted for by nonporous polymer elastomer masses each with a size of50 μm² or more.

FIG. 4 is a reference SEM photograph given as a substitute for a drawingfor showing the method for calculating the polymer elastomer coverage ina cross section of an ultrafine fiber.

DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION [Regarding theSheet-Like Article]

The sheet-like article according to embodiments of the present inventionis described first.

The sheet-like article is produced from a fibrous base material, such asnonwoven fabric, formed of ultrafine fibers and contains, as a binder, apolymer elastomer formed of resin having a hydrophilic group, such aswater-dispersed polyurethane.

As the fiber that constitutes the fibrous base material, it is possibleto employ a fiber made up of a melt-spinnable thermoplastic resin suchas polyesters, including polyethylene terephthalate, polybutyleneterephthalate, polytrimethylene terephthalate, and polylactic acid,polyamides, including 6-nylon and 66-nylon, and others including acryl,polyethylene, polypropylene, and thermoplastic cellulose fibers.Particularly, it is preferable to use polyester fibers from theviewpoint of strength, dimensional stability, and light resistance.Furthermore, the fibrous base material may be composed of a mixture offibers of different materials.

As for the cross-sectional shape of the ultrafine fibers, a circularcross section is suitable though fibers having cross sections ofnon-circular shapes such as an ellipse, flat shape, polygon such astriangle, fan, and cross may also be adopted.

The average single fiber diameter of the ultrafine fibers constituting afibrous base material is preferably 0.1 to 7 μm. Controlling the averagesingle fiber diameter at preferably 7 μm or less, more preferably 6 μmor less, and still more preferably 5 μm or less, makes it possible toobtain a sheet-like article having high softness and good raised hairquality. On the other hand, controlling the average single fiberdiameter at preferably 0.1 μm or more, more preferably 0.3 μm or more,still more preferably 0.7 μm or more, and particularly more preferably 1μm or more, ensures high post-dyeing color development performance, highfiber dispersibility during hair raising treatment by grinding withsandpaper or the like, and easy untangling.

As for the configuration of a fibrous base material formed of ultrafinefibers, it is possible to adopt a fibrous base material in the form ofwoven, knitted, nonwoven fabric or the like. Among others, the use ofnonwoven fabric is preferable because the sheet-like article will havegood surface quality after being subjected to surface hair raisingtreatment.

As the nonwoven fabric, either short-fiber nonwoven fabric or long-fibernonwoven fabric may be used, but from the viewpoint of texture andquality, the use of short-fiber nonwoven fabric is preferable.

The short fibers in the short-fiber nonwoven fabric preferably have afiber length of 25 mm or more and 90 mm or less, more preferably 35 mmor more and 75 mm or less. Controlling the fiber length at 25 mm or moremakes it possible to obtain a sheet-like article having high abrasionresistance attributed to entanglement. Furthermore, controlling thefiber length at 90 mm or less makes it possible to obtain a sheet-likearticle with improved texture and quality.

In the case of a nonwoven fabric formed of a fibrous base material ofultrafine fibers, the nonwoven fabric preferably has a structure formedof bundles of ultrafine fibers (fiber bundles) that are entangledtogether. The entanglement of bundles of ultrafine fibers allows thesheet-like article to have improved strength. Such a nonwoven fabric canbe produced by entangling ultrafine fiber-developing type fibers firstand then converting them into ultrafine fibers.

In the case of a nonwoven fabric formed of ultrafine fibers or bundlesthereof, woven or knitted fabrics may be added into the nonwoven fabricwith the aim of, for example, increasing the strength. Fibersconstituting such woven or knitted fabrics preferably have an averagesingle fiber diameter of about 0.1 to 10 μm.

For the sheet-like article according to the present invention, usefulhydrophilic group containing resins, or elastic polymers, that can beused as a binder include water-dispersed silicone resins,water-dispersed acrylic resins, and water-dispersed urethane resins, andcopolymers thereof, of which water-dispersed polyurethanes arepreferable from the viewpoint of texture.

The polyurethane is preferably a resin produced through reaction among apolymeric polyol having a number average molecular weight of preferably500 or more and 5,000 or less, an organic polyisocyanate, and a chainextender. In addition, a compound containing an active hydrogencomponent having a hydrophilic group may be combined to increase thestability of the water-dispersed polyurethane dispersion liquid. The useof a polymeric polyol having a number average molecular weight of 500 ormore, more preferably 1,500 or more, prevents the texture fromstiffening, and the use of one having a number average molecular weightof 5,000 or less, more preferably 4,000 or less, serves to maintain astrength required for a polyurethane binder.

Of the polymeric polyols described above, useful polyether based polyolsinclude those produced by addition and polymerization of such monomersas ethylene oxide, propylene oxide, butylene oxide, styrene oxide,tetrahydrofuran, epichlorohydrin, and cyclohexylene, using a polyhydricalcohol, polyamine, or the like as initiator, and those produced by ringopening polymerization of the monomers listed above using a catalystsuch as proton acid, Lewis acid, and cationic catalyst. Specificexamples include polyethylene glycol, polypropylene glycol,polytetramethylene glycol, and copolymer polyols produced by combinationthereof.

Useful polyester based polyols include, for example, polyester polyolsproduced by condensation of a low molecular weight polyol and apolybasic acid, and polyols produced by ring opening polymerization of alactone or the like.

Such low molecular weight polyols include linear alkylene glycols suchas ethylene glycol, 1,3-propylene glycol, 1,4-butanediol,1,5-pentanediol, 1,6-hexanediol, 1,7-heptanediol, 1,8-octanediol,1,9-nonanediol, and 1,10-decanediol; branched alkylene glycols such asneopentyl glycol, 3-methyl-1,5-pentanediol, 2,4-diethyl-1,5-pentanediol,and 2-methyl-1,8-octanediol; alicyclic diols such as1,4-cyclohexanediol; and aromatic divalent alcohols such as1,4-bis(β-hydroxyethoxy) benzene, which may be used singly or as acombination of two or more thereof. Furthermore, an adduct which isformed by adding one of various alkylene oxides to bisphenol A may alsobe used as the low molecular weight polyol.

Furthermore, for example, one or a plurality selected from the followingcan be used as the polybasic acid: succinic acid, maleic acid, adipicacid, glutaric acid, pimelic acid, suberic acid, azelaic acid, sebacicacid, dodecane dicarboxylic acid, phthalic acid, isophthalic acid,terephthalic acid, and hexahydroisophthalic acid.

Useful polylactone polyols include those polylactone polyols producedfrom one or a plurality selected from γ-butyrolactones,γ-valerolactones, and ε-caprolactones by ring opening polymerizationusing a polyhydric alcohol as initiator.

Useful polycarbonate based polyols include compounds produced throughreaction between a polyol and a carbonate compound such as dialkylcarbonate and diaryl carbonate.

Polyols useful as material for producing a polycarbonate polyol includethose polyols listed previously as material for producing polyesterpolyol. Useful dialkyl carbonates include dimethyl carbonate and diethylcarbonate and useful diaryl carbonates include diphenyl carbonate.

For the polymer elastomers containing a hydrophilic group to be used forthe present invention, suitable components used to add a hydrophilicgroup to a polymer elastomer include, for example, hydrophilicgroup-containing active hydrogen components. Such hydrophilicgroup-containing active hydrogen components include compounds thatcontain a nonionic group and/or anionic group and/or cationic group andan active hydrogen. Such compounds having a nonionic group and an activehydrogen include those compounds having two or more active hydrogencomponents or two or more isocyanate groups and having a side chain thatcontains a polyoxyethylene glycol group with a molecular weight of 250to 9,000, as well as triols such as trimethylolpropane andtrimethylolbutane.

Such compounds having an anionic group and an active hydrogen includecarboxyl group-containing compounds such as 2,2-dimethylol propionicacid, 2,2-dimethylol butane acid, 2,2-dimethylol valeric acid, andderivatives thereof; sulfonic group-containing compounds such as1,3-phenylene diamine-4,6-disulfone acid, 3-(2,3-dihydroxypropoxy)-1-propane sulfonic acid, and derivatives thereof; and saltsproduced by neutralizing these compounds with a neutralization agent.

Such compounds containing a cationic group and an active hydrogeninclude tertiary amino group-containing compounds such as 3-dimethylaminopropanol, N-methyl diethanolamine, N-propyl diethanolamine, andderivatives thereof.

These active hydrogen components containing a hydrophilic group may beused in the form of salts after neutralization with a neutralizationagent.

From the viewpoint of mechanical strength and dispersion stability ofpolyurethane resin, the hydrophilic group-containing active hydrogencomponent of the polyurethane molecule is preferably 2,2-dimethylolpropionic acid, 2,2-dimethylol butanic acid, or a neutralized saltthereof.

If a hydroxyl group, sulfonic group, carboxyl group, etc., selectedparticularly from the aforementioned hydrophilic group containing activehydrogen components, are introduced into polyurethane, it serves notonly to enhance the hydrophilicity of the polyurethane molecule, but ifa crosslinking agent as described later is added, it also serves toimprove the physical properties by allowing the polyurethane molecule toform a three dimensional crosslinked structure. For the production,therefore, it is preferable to use an appropriate one selected from theaforementioned hydrophilic group containing active hydrogen components.

Useful chain extenders include those compounds used in conventionalpolyurethane production processes and in particular, it is preferable touse a low molecular weight compound containing, in its molecule, two ormore active hydrogen atoms that can react with an isocyanate group andhaving a molecular weight of 600 or less. Specific examples includediols such as ethylene glycol, propylene glycol, 1,4-butanediol,1,6-hexanediol, 3-methyl-1,5-pentanediol, neopentyl glycol,1,4-cyclohexanediol, and xylylene diglycol; triols such astrimethylolpropane and trimethylol butane; diamines such as hydrazine,ethylene diamine, isophorone diamine, piperazine, 4,4′-methylenedianiline, tolylene diamine, xylylene diamine, hexamethylene diamine,and 4,4′-dicyclohexylmethane diamine; triamines such as diethylenetriamine; and aminoalcohols such as aminoethyl alcohol and aminopropylalcohol.

Useful organic polyisocyanates include aliphatic diisocyanates such ashexamethylene diisocyanate; alicyclic diisocyanates such as isophoronediisocyanate (hereinafter occasionally abbreviated as IPDI),hydrogenated xylylene diisocyanate, and dicyclohexylmethane diisocyanate(hereinafter occasionally abbreviated as MDI); aromatic/aliphaticdiisocyanates such as xylylene diisocyanate (hereinafter occasionallyabbreviated as XDI) and tetramethyl-m-xylylene diisocyanate; andaromatic diisocyanates such as tolylene diisocyanate (hereinafteroccasionally abbreviated as TDI), 4,4′-diphenyl methane diisocyanate(hereinafter occasionally abbreviated as MDI), tolidine diisocyanate,and naphthalene diisocyanate (hereinafter occasionally abbreviated asNDI).

Introducing a sulfonic group, a carboxyl group, a hydroxyl group, or aprimary or secondary amino group into the polyurethane to be used forthe present invention and adding a crosslinking agent reactive to thesefunctional group into a dispersion liquid of the polyurethane serve toproduce a resin that has an increased molecular weight and an increasedcrosslink density after reaction. Accordingly, the durability, weatherresistance, heat resistance, and wet strength retention rate can befurther improved.

Useful crosslinking agents include those having, in one molecule, two ormore reactive groups that can react with the reactive groups introducedinto the polyurethane. Specific examples of such crosslinking agentsinclude polyisocyanate based crosslinking agents such as water-solubleisocyanate compounds and blocked isocyanate compounds, melamine basedcrosslinking agents, oxazoline based crosslinking agents, carbodiimidebased crosslinking agents, aziridine based crosslinking agents, epoxycrosslinking agents, and hydrazine based crosslinking agents. Thesecrosslinking agents may be used singly or as a combination of two ormore thereof.

A water-soluble isocyanate based compound contains a two or moreisocyanate groups in a molecule, and examples include the aforementionedorganic polyisocyanate-containing compounds. Commercial products includethe Bayhydur (registered trademark) series and the Desmodur (registeredtrademark) series manufactured by Bayer MaterialScience.

A blocked isocyanate based compound contains a two or more blockedisocyanate groups in a molecule. A blocked isocyanate group is producedby blocking an organic polyisocyanate compound as described above with ablocking agent, which is, for example, an alcohol, amine, phenol, imine,mercaptan, pyrazole, oxime, or active methylene. Commercial productsthereof include the Elastron (registered trademark) series manufacturedby Dai-lchi Kogyo Seiyaku Co., Ltd., the Duranate (registered trademark)series manufactured by Asahi Kasei Chemicals Corporation, and theTakenate (registered trademark) series manufactured by Mitsui Chemicals,Inc.

Useful melamine based crosslinking agents include compounds containingtwo or more methylol groups or methoxy methylol groups in a molecule.Commercial products thereof include the Yuban (registered trademark)series manufactured by Mitsui Chemicals, Inc., the Cymel (registeredtrademark) series manufactured by Nihon Cytec, and the Sumimal(registered trademark) series manufactured by Sumitomo Chemical Co.,Ltd.

Useful oxazoline based crosslinking agents include compounds containingtwo or more oxazoline groups (oxazoline backbone) in a molecule.Commercial products thereof include the Epocros (registered trademark)series manufactured by Nippon Shokubai Co., Ltd. Useful carbodiimidebased crosslinking agents include compounds containing two or morecarbodiimide groups in a molecule. Commercial products thereof includethe Carbodilite (registered trademark) series manufactured by NisshinboIndustries, Inc.

Useful epoxy based crosslinking agents include compounds containing twoor more epoxy groups in a molecule. Commercial products thereof includethe Denacol (registered trademark) series manufactured by Nagase ChemteXCorporation, diepoxy-polyepoxy based compounds manufactured by SakamotoYakuhin Kogyo Co., Ltd., and the Epicron (registered trademark) seriesmanufactured by DIC.

Useful aziridine based crosslinking agents include compounds containingtwo or more aziridinyl groups in a molecule. Useful hydrazine basedcrosslinking agents include hydrazine and compounds containing two ormore hydrazine groups (hydrazine backbone) in a molecule.

Among others, preferable functional groups contained in polyurethaneinclude hydroxyl group and/or carboxyl group and/or sulfonic group, andpreferable crosslinking agents include polyisocyanate based crosslinkingagents and carbodiimide compounds. Furthermore, the combined use of acarbodiimide compound and a polyisocyanate based crosslinking agentenhances the crosslinked structure of the polyurethane resin and inaddition, enhances the moist heat resistance improving effect whilemaintaining flexibility.

Water-dispersed polyurethane compounds generally contain a hydrophilicgroup in the molecular structure and accordingly, they are higher inaffinity with water molecules and more liable to swelling and relaxationof the polyurethane's molecular structure in a wet environment thanconventional organic solvent based polyurethanes. In a wet environment,therefore, they tend to fail to maintain good physical properties thatthey have in a dry environment. Compared to this, the use of theaforementioned crosslinking agents serves to enhance the moist heatresistance improving effect, making it possible to provide a sheet withhigh tensile strength in a wet environment. As a result, structuralchanges of the polyurethane molecule likely to be caused by water in thedyeing step can be depressed and the morphological stability of thesheet-like article and strong contact between polyurethane and fibrousbase material can be maintained, thereby achieving high quality withgood physical properties and a uniform feel.

Carbodiimide crosslinking agents show high crosslinking reactivity atlow temperatures of 100° C. or less and they are adopted favorably fromthe viewpoint of productivity. Besides reacting mainly with the hydroxylgroup, the isocyanate compound and/or blocked isocyanate compound reactactively with the urethane bond and/or urea bond in the hard segment(HS) part in polyurethane at high temperatures, particularly in thetemperature range of 120° C. or more and 200° C. or less, preferably inthe temperature range of 140° C. or more and 200° C. or less, to form anallophanate bond or burette bond, leading to the development of astronger crosslinked structure and a distinct microphase separationstructure of polyurethane.

It is preferable for the polyurethane film according to the presentinvention to have a storage elastic modulus E′ of 1 to 100 MPa, morepreferably 2 to 50 MPa, at a temperature of 20° C. from the viewpoint offlexibility and impact resilience. The loss elastic modulus ispreferably 0.1 MPa to 20 MPa, more preferably 0.5 MPa to 12 MPa.Furthermore, tan δ is preferably 0.01 to 0.4, more preferably 0.02 to0.35.

For the present invention, the storage elastic modulus E′ and tan δ aredetermined for a polyurethane film (film) with a film thickness of 200μm using a storage elastic modulus measuring apparatus (DMA7100,manufactured by Hitachi High-Tech Science Corporation) at a frequency of12 Hz. Here, tan δ is calculated as E″/E′ (E″ represents the losselastic modulus).

E′ indicates the elastic nature of polyurethane resin. The fold andcrease recoverability of a sheet-like article decreases with adecreasing E′ while the texture of the sheet-like article deteriorateswith an increasing E′.

On the other hand, tan δ, which is calculated as E″/E′ (where E″ is theloss elastic modulus and represents the viscosity), means the proportionof the viscosity relative to that of the polyurethane. As in the case ofE′, the fold and crease recoverability of a sheet-like article decreaseswith a decreasing tan δ while the texture of the sheet-like articlebecomes stiffer with an increasing E′.

It is preferable that the density of the sheet-like article according tothe present invention is 0.2 to 0.7 g/cm³. The density is morepreferably 0.2 g/cm³ or more and still more preferably 0.25 g/cm³ ormore. A density of 0.2 g/cm³ or more ensures a dense surface appearanceand high quality. On the other hand, if a sheet-like article has adensity of preferably 0.7 g/cm³ or less, more preferably to 0.6 g/cm³ orless, it serves to prevent the texture of the sheet-like article frombecoming stiff.

It is preferable for the polyurethane in the sheet-like articleaccording to the present invention to account for 10% to 80% by mass. Ifthe content of the polyurethane is 10 mas % or more, more preferably 15mass % or more, a sufficient sheet strength can be obtained and fiberscan be prevented from falling off. Furthermore, if the content of thepolyurethane is 80% by mass or less, more preferably 70% by mass orless, the texture can be prevented from becoming stiff and good raisedhair quality can be obtained.

For the sheet-like article according to embodiments of the presentinvention, a porous structure is produced from water-dispersedpolyurethane (elastic polymer) and high fold and crease recoverabilityand flexibility closely equivalent to those of artificial leatherproducts produced from solvent based polyurethane is realized byadopting an elastic polymer such as water-dispersed polyurethane,preparing a liquid by adding a viscosity improver to an aqueousdispersion of the water-dispersed polyurethane and other components, andcoagulating it in hot water.

Thus, the present invention aims to provide a sheet-like articlecomprising a fibrous base material formed of ultrafine fibers and/orultrafine fiber bundles provided with, as a binder, a polymer elastomerhaving a hydrophilic group, any thickness-directional cross section ofthe sheet-like article containing regions occupied by the polymerelastomer, the regions including independent regions each with across-sectional area of 50 μm² or more, the total area of theindependent regions accounting for 0.1% or more and 5.0% or less of thecross-sectional area of the artificial leather in an observation viewfield.

In a preferred embodiment, the present invention provides a sheet-likearticle that includes a fibrous base material formed of ultrafine fibersand/or ultrafine fiber bundles and, as a binder, a polymer elastomerhaving a hydrophilic group, wherein 1% or more and 35% or less of thecircumferences of the cross sections of the ultrafine fibers and/orultrafine fiber bundles observed in a cross section made by cutting thesheet-like article in the thickness direction is covered by film of thepolymer elastomer.

[Method for Producing Sheet-Like Articles]

Described below are production methods for the sheet-like articleaccording to embodiments of the present invention.

As the fibrous base material for use in the invention, fabrics such aswoven fabric, knitted fabric, and nonwoven fabric can be adoptedfavorably. Among others, the use of nonwoven fabric is preferablebecause the sheet-like article will have good surface quality afterbeing subjected to surface hair raising treatment. The fibrous basematerial for use in the invention may be a laminate containing layers ofthese woven fabric, knitted fabric, and nonwoven fabric.

The nonwoven fabric for use in the invention may be either short-fibernonwoven fabric or long-fiber nonwoven fabric, but short-fiber nonwovenfabric is preferred because good surface quality attributed to raisedhairs with a uniform length is obtained.

The short fibers in the short-fiber nonwoven fabric preferably have afiber length of 25 mm to 90 mm, more preferably 35 mm to 75 mm. A fiberlength of 25 mm or more makes it possible to obtain a sheet-like articlethat has high abrasion resistance due to entanglement. Furthermore,controlling the fiber length at 90 mm or less makes it possible toobtain a sheet-like article with further improved quality.

As the fiber that constitutes the fibrous base material, it is possibleto employ a fiber made up of a melt-spinnable thermoplastic resin suchas polyesters such as polyethylene terephthalate, polybutyleneterephthalate, polytrimethylene terephthalate, and polylactic acid;polyamides such as 6-nylon and 66-nylon; and others such as acryl,polyethylene, polypropylene, and thermoplastic cellulose. Particularly,it is preferable to use polyester fibers from the viewpoint of strength,dimensional stability, and light resistance. Furthermore, the fibrousbase material may be composed of a mixture of fibers of differencematerials.

The cross-sectional shape of fiber used for the present invention may becircular, and it also may be a deformed shape such as ellipse, flat,polygonal such as triangular, fan-shaped and cross.

The average fiber diameter of the fibers constituting a fibrous basematerial is preferably 0.1 to 7 μm, more preferably 0.3 to 5 μm. Anaverage fiber diameter of the fibers of 7 μm allows the fibrous basematerial to have a more flexible feel. An average fiber diameter of thefibers of 0.1 μm or more, on the other hand, ensures improved colordevelopment after dyeing.

In the case where the fibrous base material used for the presentinvention is a nonwoven fabric, it is preferable to combine a wovenfabric or a knitted fabric with the nonwoven fabric in order to improvestrength and the like. The combination of the nonwoven fabric with awoven fabric or knitted fabric may be achieved by laminating thenonwoven fabric with a woven fabric or knitted fabric, or inserting awoven fabric or knitted fabric into the nonwoven fabric. Among others,it is preferable to use a woven fabric from the viewpoint of expectedimprovement in morphological stability and resistance.

Single yarns (warp and weft) that constitute the woven fabric or knittedfabric may be those of synthetic fiber such as polyester fiber andpolyamide fiber, but they are preferably threads of the same fibermaterial as the ultrafine fibers that finally constitute the cloth suchas nonwoven fabric.

With respect to the type of these single yarns, they may be filamentyarns or spun yarns, and they are preferably in a hard twist form. Inparticular, the use of filament yarns is preferable because spun yarnsare likely to suffer a loss of surface fuzzing.

When hard twist yarns are to be used, their twist count is preferably1,000 T/m or more and 4,000 T/m or less, more preferably 1,500 T/m ormore and 3,500 T/m or less. If the twist count is less than 1,000 T/m,the hard twist yarns will suffer more frequent breakage of constituentsingle fibers during the needle punching treatment, leading to productswith deteriorated physical characteristics and exposure of many singlefibers exposed from the product surface. If the twist count is more than4,000 T/m, on the other hand, breakage of single fibers can bedepressed, but the hard twist yarns that constitute the woven fabric orknitted fabric will become too stiff, tending to results in a hardtexture.

For the invention, furthermore, the use of ultrafine fiber-developingtype fibers as fibrous base material is preferable. The use of ultrafinefiber-developing type fibers in fibrous base material serves for stableformation of entangled bundles of the ultrafine fibers described above.

In the case where the fibrous base material is a nonwoven fabric, it ispreferable for the nonwoven fabric to have a structure formed by theentanglement of bundles (fiber bundles) of ultrafine fibers. Theentanglement of bundles of ultrafine fibers allows the sheet-likearticle to have improved strength. Such a nonwoven fabric can beproduced by entangling ultrafine fiber-developing type fibers first andthen converting them into ultrafine fibers.

Adoptable ultrafine fiber-developing type fibers include: island-in-seatype composite ones produced by using two thermoplastic resins differentin solubility in a solvent as sea component and island component anddissolving and removing the sea component by using a solvent or the liketo allow the island component to be left to form ultrafine fibers; andsplittable type composite ones produced by alternately disposing twothermoplastic resins, radially or in layers, in the cross sectionthereof and splitting and separating the two components to formultrafine fibers.

In particular, island-in-sea type composite fibers are preferred fromthe viewpoint of the flexibility and texture of the resulting sheet-likearticle because the removal of the sea regions will leave moderate gapsamong island regions, i.e., among ultrafine fibers.

Island-in-sea type composite fibers include island-in-sea type compositefibers produced by using a spinneret designed for island-in-sea typecomposite fibers to spin fibers in which two components, i.e. sea andisland, are mutually arrayed, and blend-spun fibers produced by spinninga mixture of two components for sea and island, of which theisland-in-sea type composite fibers have been used favorably becausethey can serve to produce ultrafine fibers with uniform fineness andalso produce ultrafine fibers with an adequate length to ensure theproduction of a sheet-like article with increased strength.

Usable materials for the sea component of island-in-sea type compositefibers include polyethylene, polypropylene, polystyrene, polyestercopolymers of sodium sulfoisophthalic acid, polyethylene glycol, or thelike, polylactic acid, and polyvinyl alcohol. Particularly preferableare copolymerized polyester and polylactic acid produced from, forexample, sodium sulfoisophthalic acid and polyethylene glycol, both ofwhich are alkali resolvable and capable of being decomposed withoutusing an organic solvent, and also preferable is polyvinyl alcohol thatis soluble in hot water.

With respect to the ratio (proportion) between the sea component and theisland component in island-in-sea type composite fiber, it is preferablefor the island fiber to account for 0.2 to 0.9 by mass, more preferably0.3 to 0.8, of the island-in-sea type composite fiber. If the mass ratiobetween the sea component and the island component is 0.2 or more, thisensures a small sea component removal ratio and leads to improvedproductivity. If the mass ratio is 0.9 or less, the fiber-openingcapability of the island fiber will improve, and confluence of streamsof the island component can be prevented. The number of island componentstreams can be controlled by appropriately adjusting the spinneretdesign.

The maximum diameter of each single fiber that constitutes the ultrafinefiber-developing type fiber, such as island-in-sea type composite fiber,is preferably 5 to 80 μm, more preferably 10 to 50 μm. If the maximumdiameter of each single fiber is less than 5 μm, the fiber will be lowin strength and tends to suffer single fiber breakage during treatmentsteps such as needle punching as described later. If the maximumdiameter of each single fiber is less than 80 μm, on the other hand,treatment steps such as needle punching may fail to produce entanglementefficiently.

Usable methods for obtaining a nonwoven fabric to be used as fibrousbase material for the present invention include the method of entanglinga fiber web by needle punching or water jet punching, as well as thespun-bond method, melt-blow method, paper making method. In particular,methods containing a needle punching or water jet punching step are usedfavorably in order to obtain such ultrafine fiber bundles as describedabove.

To produce an integrated laminate of a woven fabric or knitted fabricand a nonwoven fabric to be used as fibrous base material, needlepunching treatment, water jet punching treatment, etc., are usedfavorably from the viewpoint of efficient entanglement of fibers. Inparticular, needle punching treatment is used favorably from theviewpoint of orienting the fibers in the vertical direction of thefibrous base material regardless of the thickness of the sheet.

The needle used for needle punching treatment preferably has 1 to 9barbs. The use of at least one needle barb allows fibers to be entangledefficiently. The use of 9 or less needle barbs, on the other hand,prevents fibers from being damaged significantly. The use of more than 9needle barbs will lead to significant fiber damage and deterioration inproduct appearance due to needle marks left on the fibrous basematerial.

If a nonwoven fabric is to be integrated with a woven fabric or knittedfabric by entanglement, it is preferable for the nonwoven fabric to havepreliminary entanglement, which serves to prevent significant creasegeneration when combining the nonwoven fabric with a woven fabric orknitted fabric by needle punching treatment. If such preliminaryentanglement by needle punching treatment is adopted, it is effectivewhen performed with a punching density of 20 punches/cm² or more. It ispreferable for the preliminary entanglement to be performed with apunching density of 100 punches/cm² or more, and it is more preferablefor the preliminary entanglement to be performed with a punching densityof 300 punches/cm² to 1,300 punches/cm².

This is because if the punching density preliminary entanglement is lessthan 20 punches/cm², the width of the nonwoven fabric can be decreasedduring the steps of entanglement with a woven fabric or knitted fabricand subsequent needle punching treatment, possibly making it impossibleto obtain a fibrous base material with a smooth surface due to creasesin the woven fabric or knitted fabric attributable to changes in thewidth. If the punching density preliminary entanglement is more than1,300 punches/cm², on the other hand, the entanglement in the nonwovenfabric itself proceeds to an excessive degree and the fibers will not beable to move easily to realize sufficient entanglement with the fibersin the woven fabric or knitted fabric, which is disadvantageous forachieving a perfectly integrated structure in which the nonwoven fabricand the woven fabric or knitted fabric are entangled strongly.

When fibers are entangled by needle punching treatment for the presentinvention, the punching density is preferably in the range of 300punches/cm² to 6,000 punches/cm², more preferably 1,000 punches/cm² to3,000 punches/cm², regardless of whether a woven fabric or knittedfabric exists or not.

To get a nonwoven fabric entangled with a woven fabric or knittedfabric, woven fabric or knitted fabric layers are laid over one or bothsides of the nonwoven fabric, or woven fabric or knitted fabric layersare inserted between a plurality of nonwoven fabric layers, followed byneedle punching to cause entanglement of fibers to provide a fibrousbase material.

When performing water jet punching, it is preferable to use water in acolumnar form. Specifically, water is preferably squirted through anozzle with a diameter of 0.05 to 1.0 mm under a pressure of 1 to 60 MPa.

The nonwoven fabric formed of ultrafine fiber-generating type fibersprocessed by needle punching or water jet punching preferably has anapparent density of 0.13 to 0.45 g/cm³, more preferably 0.15 to 0.30g/cm³. An apparent density of 0.13 g/cm³ or more makes it possible toproduce artificial leather having sufficiently high morphologicalstability and dimensional stability. An apparent density of 0.45 g/cm³or less, on the other hand, serves to maintain adequate spaces toaccommodate a polymer elastomer.

The thickness of the fibrous base material is preferably 0.3 mm or moreand 6.0 mm or less, more preferably 1.0 mm or more and 3.0 mm or less.If the thickness of the fibrous base material is less than 0.3 mm, theresulting sheet-like article may suffer from poor morphologicalstability. A thickness of more than 6.0 mm tends to lead to frequentoccurrence of needle breakage in the needle punching step.

To ensure a denser surface, the nonwoven fabric formed of ultrafinefiber-generating type fibers obtained as described above may be shrunkenby dry heat and/or wet heat to achieve a higher fiber density.

When using island-in-sea type composite fiber, the sea removal treatmentintended to remove the sea component from the fiber may be performedeither before or after adding a water-dispersed polyurethane dispersionliquid, which contains water-dispersed polyurethane, to the fibrous basematerial. If the sea removal treatment is carried out before theaddition of the water-dispersed polyurethane dispersion liquid, theabrasion resistance of the sheet-like article increases because astructure in which the water-dispersed polyurethane adheres directly tothe ultrafine fibers is easily formed so that the ultrafine fibers canbe firmly held.

On the other hand, if inhibitory agents such as cellulose derivativesand polyvinyl alcohol (hereinafter occasionally abbreviated as PVA) areadded together with ultrafine fibers before adding a water-dispersedpolyurethane dispersion liquid, followed by adding a water-dispersedpolyurethane dispersion liquid, the contact between the ultrafine fibersand polyurethane resin can be weakened to achieve a more flexibletexture.

The aforementioned addition of inhibitory agents may be performed eitherbefore or after subjecting the sea-island structure fiber to sea removaltreatment. The addition of inhibitory agents before sea removaltreatment works to enhance the morphology retention capability of thefibrous base material even if the metsuke (weight per unit surface area)of the fiber decreases to cause a decline in the tensile strength of thesheet. Accordingly, this ensures not only stable processing of thinsheets, but also an increase in thickness retention capability of thefibrous base material during the sea removal treatment step, serving toprevent the density of the fibrous base material from increasing. On theother hand, adding inhibitory agents after sea removal treatment worksto increase the density of the fibrous base material. Either of theprocedures should be adopted to meet particular purposes.

PVA is used favorably as an inhibitory agent because it serveseffectively to reinforce the fibrous base material and will not bedissolved easily in water. Of the various types of PVA, particularlypreferable is the use of a highly saponified, water-insoluble PVAbecause the inhibitory agent will not be dissolved easily in water whena water-dispersed polyurethane dispersion liquid is added and alsobecause the contact between ultrafine fibers and polyurethane can beimpeded effectively.

For the highly saponified PVA, the degree of saponification ispreferably 95% or more and 100% or less, more preferably 98% or more and100% or less. If the degree of saponification is 95% or more, thedissolution of the water-dispersed polyurethane dispersion liquid duringits addition is depressed.

The PVA preferably has a degree of polymerization of 500 or more and3,500 or less, more preferably 500 or more and 2,000 or less. If thedegree of polymerization of the PVA is 500 or more, the highlysaponified PVA will not undergo significant dissolution during theaddition of the polyurethane dispersion liquid. If the degree ofpolymerization of the PVA is less than 3,500, on the other hand, thesolution of highly saponified PVA will not become too high in viscosityand the addition of the highly saponified PVA to the fibrous basematerial can be performed stably.

The quantity of the PVA to be added is preferably 0.1 mass % to 80 mass%, more preferably 5 mass % or more 60 mass % or less, relative to thequantity of the fibrous base material that will remain in the finalproduct. If the quantity of the highly saponified PVA added is 0.1 mass% or more, the morphological stability is maintained high during the searemoval treatment step and poor contact between ultrafine fibers andpolyurethane can be prevented. If the quantity of the highly saponifiedPVA added is 80 mass % or less, the contact between ultrafine fibers andpolyurethane will not become too poor and uniform raised hairs will beformed, serving to provide a product with uniform surface quality.

To add an inhibitory agent as described above to the fibrous basematerial, the process of dissolving the inhibitory agent in water,impregnating the fibrous base material with it, and heat-drying it isused favorably because this allows the inhibitory agent to be addeduniformly. With respect to the drying temperature, a long drying timewill be necessary if the temperature is too low whereas the inhibitoryagent will be completely insolubilized and its removal by dissolutionwill become impossible if the temperature is too high. Accordingly, itis preferable for the drying temperature to be 80° C. or more and 180°C. or less, more preferably 110° C. or more and 160° C. or less. Thedrying time is preferably one minute or more and 30 minutes or less fromthe viewpoint of processability.

According to a preferred embodiment, dissolution and removal of theinhibitory agent is carried out by leaving the fibrous base materialcontaining the inhibitory agent in steam at a temperature of 100° C. ormore and in hot water at a temperature of 60° C. or more and 100° C. orless, followed by squeezing the liquid using a mangle or the like asrequired, to achieve dissolution and removal.

The sea removal treatment can be carried out by immersing the fibrousbase material containing the island-in-sea composite fiber in a solventand then squeezing the liquid. Solvents usable for dissolving the seacomponent include organic solvents such as toluene and trichloroethylenefor a sea component of polyethylene, polypropylene, or polystyrene;alkaline solutions such as aqueous sodium hydroxide solution for a seacomponent of copolymerized polyester or polylactic acid; and hot waterfor a sea component of polyvinyl alcohol.

Described next is the polyurethane to be used as a polymer elastomer forembodiments of the present invention.

If polyurethane is used in the form of particles to be dispersed in anaqueous medium, the hydrophilic group-containing active hydrogencomponent is preferably adopted as a component of the polyurethane fromthe viewpoint of dispersion stability of the polyurethane, and accordingto a more preferred embodiment, a neutralized salt should be used.

The neutralization agents that are usable for the neutralized salt of acompound containing a hydrophilic group and an active hydrogen includeamine based compounds such as trimethylamine, triethylamine, andtriethanolamine, and hydroxides such as sodium hydroxide and potassiumhydroxide.

There are no specific limitations on the timing of adding aneutralization agent to be used for a hydrophilic group-containingactive hydrogen component, and it may be added before or after thepolyurethane polymerization step, before or after the aqueous mediumdispersion step, etc., but from the viewpoint of the stability of thepolyurethane in the aqueous dispersion liquid, it is preferable to addit before the step of dispersion in an aqueous medium or during the stepof dispersion in an aqueous medium.

From the viewpoint of dispersion stability and water resistance of thepolyurethane, the content of the hydrophilic group-containing activehydrogen component and/or salts thereof is preferably 0.005 to 30 mass%, more preferably 0.01 to 15 mass %, relative to the mass of thepolyurethane.

If polyurethane is used in the form of particles to be dispersed in anaqueous medium, a surface active agent, in addition to theaforementioned hydrophilic group-containing active hydrogen component,may be used as an external emulsifier for the polyurethane to allow thepolyurethane to be dispersed in an aqueous medium.

Such surface active agents include nonionic surface active agents,anionic surface active agents, cationic surface active agents, andamphoteric surface active agents. These surface active agents may beused singly or as a combination of two or more thereof.

Useful nonionic surface active agents include alkylene oxide additiontype ones such as polyoxyethylene nonylphenyl ether, polyoxyethylenedinonylphenyl ether, polyoxyethylene lauryl ether, and polyoxyethylenestearyl ether, and polyhydric alcohol type ones such as glycerinmonostearate.

Useful anionic surface active agents include carboxylates, sulfate estersalts, sulfonates, and phosphate ester salts such as sodium laurate,sodium lauryl sulfate, lauryl ammonium sulfate, sodium dodecylbenzenesulfonate, and fatty alcohol sodium phosphate diester.

Useful cationic surface active agents include quaternary ammonium saltssuch as distearyl dimethylammonium chloride. Useful amphoteric surfaceactive agents include methyl laurylaminopropionate, lauryldimethylbetaine, and coconut fatty acid amidopropyldimethylamino aceticacid betaine.

A conventional polyurethane dispersion liquid production method may beapplied to prepare a dispersion liquid of polyurethane to be used forthe present invention. Available ones include, for example, a method inwhich a liquid polymer prepared by reacting a polyisocyanate, polyol,chain extender, and/or hydrophilic group-containing polyol as describedabove is emulsified in water in the presence of an emulsifier, a methodin which a prepolymer having an isocyanate group at an molecular end isprepared by reacting a polyisocyanate, polyol, and/or chain extender,and/or hydrophilic group-containing polyol as described above and theprepolymer is then emulsified in water in the presence of an emulsifier,while or followed by completing the chain elongation reaction using achain extender, and a method in which a polyisocyanate, polyol, and/orchain extender, and/or hydrophilic group-containing polyol as describedabove are reacted together and directly emulsified in water withoutusing an emulsifier. When polymerization is performed without formingsuch a prepolymer or when polymerization of such a prepolymer isperformed, it may be carried out in the absence of a solvent or may becarried out in the presence of an organic solvent such as methyl ethylketone, toluene, and acetone.

For example, a fibrous base material may be immersed in awater-dispersed polyurethane dispersion liquid containing thewater-dispersed polyurethane synthesized above to add the polyurethaneto the fibrous base material, followed by performing heat-drying toachieve coagulation and solidification.

For embodiments of the present invention, a water-dispersed polyurethanedispersion liquid containing a viscosity improver as described above isadded to a fibrous base material, and the water-dispersed polyurethaneis coagulated in hot water preferably at a temperature of 50° C. to 100°C., more preferably at a temperature of 60° C. to 97° C., to produce aporous structure of polyurethane.

The immersion time in hot water is preferably 10 seconds or more and 5minutes or less, more preferably 30 seconds or more and 3 minutes orless. Adjusting the immersion time in this range allows the polyurethaneto be sufficiently coagulated.

If the hot water coagulation technique is used to coagulate thepolyurethane as described above, the quantity of heat per unit timerequired for heating the polyurethane increases and accordingly thecoagulation speed becomes faster. Then, the shift of the water-dispersedpolyurethane dispersion liquid toward the fibrous base materialdecreases and accordingly, the adhesion between the fiber andpolyurethane declines, leading to a flexible texture.

If a viscosity improver is combined with the water-dispersedpolyurethane dispersion liquid, the polyurethane emulsion in thewater-dispersed polyurethane dispersion liquid used to impregnate thefibrous base material suffers suppression of the Brownian movement underthe influence of the viscosity of the liquid. Accordingly, the frequencyof contact among emulsion particles decreases, making it possible todecrease the size of polyurethane masses in the coagulation step,thereby achieving a flexible texture. In addition, the dispersion liquidwill not diffuse significantly in the hot water and the separation ofpolyurethane during the coagulation step can be depressed, serving torealize a coagulation process with a very high productivity.

If a dispersion liquid prepared by combining a viscosity improver withan aqueous dispersion liquid such as water-dispersed polyurethane iscoagulated in hot water, the film coats of the water-dispersedpolyurethane (elastic polymer) will become smaller to achieve a flexibletexture. Furthermore, the polyurethane film coats that cover the fibrousbase material become smaller in quantity to achieve a flexible texture.

Useful viscosity improvers to be added to the water-dispersedpolyurethane dispersion liquid include nonionic, anionic, cationic, andamphoteric ones. Of these, the use of a nonionic viscosity improver ispreferred.

Available viscosity improvers are divided into two groups: associationtype viscosity improvers and water-soluble polymer type viscosityimprovers. Association type viscosity improvers include urethanemodified compounds, acrylic modified compounds, and copolymer compoundsthereof, and generally known association type viscosity improvers can beapplied. Examples include urethane based association type viscosityimprovers as disclosed in Japanese Unexamined Patent Publication (Kokai)No. 2003-292937, Japanese Unexamined Patent Publication (Kokai) No.2001-254068, Japanese Unexamined Patent Publication (Kokai) No.SHO-60-49022, Japanese Unexamined Patent Publication (Kokai) No.2008-231421, Japanese Unexamined Patent Publication (Kokai) No.2002-069430, and Japanese Unexamined Patent Publication (Kokai) No.HEI-9-71766, and the association type viscosity improvers produced bycopolymerization of urethane monomers and other acrylic monomers asdisclosed in Japanese Unexamined Patent Publication (Kokai) No.SHO-62-292879 and Japanese Unexamined Patent Publication (Kokai) No.HEI-10-121030.

Useful water-soluble polymer compounds include natural polymercompounds, semisynthetic polymer compounds, and synthetic polymercompounds.

Useful natural polymer compounds include nonionic compounds such astamarind gum, guar gum, roast bean gum, tragacanth gum, starch, dextrin,gelatin, agarose, casein, and curdlan; anionic compounds such as xanthangum, carrageenan, acacia gum, pectin, collagen, sodium chondroitinsulfate, sodium hyaluronate, carboxymethyl starch, and starch phosphate;and cationic compounds such as cation starch and chitosan.

Useful semisynthetic polymer compounds include nonionic compounds suchas methyl cellulose, ethyl cellulose, hydroxyethyl cellulose, ethylhydroxyethyl cellulose, methyl hydroxypropyl cellulose, soluble starch,and methyl starch, and anionic compounds such as carboxymethylcellulose, carboxymethyl starch, and alginates.

Useful synthetic polymer compounds include nonionic compounds such aspolyvinyl alcohol, polyacrylamide, polyvinyl pyrolidone, polymethylvinyl ether, polyethylene glycol, and polyisopropyl acrylamide; anioniccompounds such as carboxyvinyl polymer, sodium polyacrylate, and sodiumpolystyrene sulfonate; and cationic compounds such as dimethylaminoethyl(meth)acrylate quaternary salts, dimethyldiallylammonium chloride,polyamidine, polyvinyl imidazoline, and polyethylene imine.

Preferable viscosity improvers for the present invention includenonionic viscosity improvers that do not have significant influence onthe stability of the water-dispersed polyurethane dispersion liquid.

The water-dispersed polyurethane dispersion liquid that contains aviscosity improver preferably show non-Newtonian properties. If thewater-dispersed polyurethane dispersion liquid is one that, in additionto being non-Newtonian, has a tendency to decrease in viscosity whenreceiving a force, its viscosity will decrease when a force is appliedby, for example, stirring and accordingly, the fibrous base materialwill be able to be impregnated uniformly with the dispersion liquid. Ifit is left to stand after the impregnation, the original viscosity willbe restored and the dispersion liquid infiltrated in the fibrous basematerial will not come off easily from the fibrous base material.

It is more preferable for the water-dispersed polyurethane dispersionliquid that contains a viscosity improver to show thixotropy. If thewater-dispersed polyurethane dispersion liquid is thixotropic, itsviscosity will decrease when a force is applied by, for example,stirring and accordingly, the fibrous base material will be able to beimpregnated uniformly with the dispersion liquid. If it is left to standafter the application of a force, the original viscosity will berestored and the dispersion liquid infiltrated in the fibrous basematerial will not come off easily from the fibrous base material.

Useful viscosity improvers that have thixotropy include some selectedappropriately from those listed above, but natural polymer compounds(polysaccharides) are used favorably because they are likely to havelarge viscosity improving effect even when added in small amounts. Morepreferable viscosity improvers include guar gum, which is high insolubility in water, high in compatibility with water-dispersedpolyurethane liquids, and high in thixotropy even when low inconcentration.

An aqueous resin dispersion liquid containing a viscosity improverpreferably has a viscosity of 200 mPa·s to 100,000 mPa·s, morepreferably 200 mPa·s to 10,000 mPa·s, and still more preferably 200mPa·s to 5,000 mPa·s. If the viscosity of the aqueous resin dispersionliquid is maintained at 200 mPa·s or more, the polyurethane can beprevented from falling off during the hot water coagulation step, whilemaintaining the viscosity at 100,000 mPa·s or less allows thewater-dispersed polyurethane dispersion liquid to infiltrate uniformlyin the fibrous base material.

The water-dispersed polyurethane dispersion liquid to be added to afibrous base material preferably contain a thermosensitive coagulantfrom the viewpoint of depressing the migration of the polyurethaneduring the polyurethane coagulation step to allow the polyurethane toinfiltrate uniformly in the fibrous base material.

Useful thermosensitive coagulants include inorganic salts such as sodiumsulfate, magnesium sulfate, calcium sulfate, calcium chloride, magnesiumchloride, and calcium chloride; and ammonium salts such as sodiumpersulfate, potassium persulfate, ammonium persulfate, and ammoniumsulfate. They may be used singly or as a combination of two or morethereof in an appropriately adjusted amount. The water-dispersedpolyurethane coagulation temperature is adjusted and then thewater-dispersed polyurethane dispersion liquid is destabilized byheating so that it will be coagulated.

The aforementioned thermosensitive coagulation temperature of awater-dispersed polyurethane dispersion liquid is preferably 40° C. to90° C., more preferably 50° C. to 80° C., from the viewpoint of storagestability and texture of the processed fiber product.

In addition to the crosslinking agents and thermosensitive coagulantsdescribed above, the polyurethane dispersion liquid may further containother various additives as mentioned below.

Examples of these additives include pigments such as carbon black;weathering stabilization agents such as antioxidants (hindered phenolicbased, sulfur based, and phosphorous based antioxidants), ultravioletabsorbers (benzotriazole based, triazine based, benzophenone based, andbenzoate based ultraviolet absorbers), and hindered amine basedphotostabilizers); and others including flexible water repellent agents(polysiloxane, modified silicone oil, other silicone compounds, polymerbased on fluoroalkyl esters of acrylic acids, and other fluorinecompound based flexible water repellent agents), wetting agents(ethylene glycol, diethylene glycol, propylene glycol, glycerin, andother similar wetting agents), antifoam agents (octyl alcohol, sorbitanmonooleate, polydimethyl siloxane, polyether modified silicone, andfluorine modified silicone, and other similar antifoam agents), fillers(fine particles of calcium carbonate, titanium oxide, silica, talc,ceramics, or resin, hollow beads, and other similar fillers), flameretardants (halogen based, phosphorus based, antimony based, melaminebased, guanidine based, guanylurea based, silicone based, and otherinorganic flame retardants), microballoons (such as MatsumotoMicrosphere (registered trademark) manufactured by MatsumotoYushi-Seiyaku Co., Ltd.), foaming agents [examples includedinitrosopentamethylene tetramine (such as Celmike A (registeredtrademark) manufactured by Sankyo Kasei Co., Ltd.), azodicarbonamide(such as Celmike CAP (registered trademark) manufactured by Sankyo KaseiCo., Ltd.), p,p′-oxy bisbenzenesulfonyl hydrazide (such as Celmike S(registered trademark) manufactured by Sankyo Kasei Co., Ltd.),N,N′-dinitrosopentamethylene tetramine (such as Cellular GX (registeredtrademark) manufactured by Eiwa Chemical Ind. Co., Ltd.), other organicfoaming agents, sodium hydrogen carbonates (such as Celmike 266(registered trademark) manufactured by Sankyo Kasei Co., Ltd.), andother inorganic foaming agents],

2,2′-azobis[2-methyl-N-(2-hydroxyethyl) propione amide] (such as VA-086manufactured by Wako Pure Chemical Industries, Ltd.), viscosityadjustors, plasticizers (phthalic esters, adipic esters, etc.), and moldreleasing agents (wax based, metal soap based, and their mixture basedmold releasing agents).

According to a preferred embodiment, additional heating (for curing) isperformed after the infiltration and coagulation of the water-dispersedpolyurethane dispersion liquid in a fibrous base material, in order topromote the fusion bonding of the water-dispersed polyurethane emulsionand allow the polyurethane to form a proper molecular structure, therebyimproving the moist heat resistance. Curing may be carried out bycontinuous coagulation and curing steps after infiltrating thewater-dispersed polyurethane dispersion liquid in a fibrous basematerial, or by a separate curing step performed after infiltrating andcoagulating the water-dispersed polyurethane dispersion liquid in afibrous base material.

In regard to the drying temperature, a long drying time is required atlow drying temperatures while heat decomposition of the polyurethane isaccelerated at high temperatures, and therefore, the drying is performedpreferably at a temperature of 80° C. or more and 200° C. or less, morepreferably at 120° C. or more and 190° C. or less, still more preferably150° C. or more and 180° C. or less.

From the viewpoint of processability, the drying time is preferably 1minute or more and 60 minutes or less, more preferably 1 minute or moreand 30 minutes or less. For embodiments of the present invention,completing the curing step quickly at a high temperature ensures anincrease in the flowability of the polyurethane molecules, an increasein the coagulation rate of the hard segment (HS) parts and the formationof a distinct microphase separation structure between the hard segment(HS) parts and the soft segment (SS) parts in the molecular structurewhich consists of hard segment (HS) parts formed mainly of urethanegroups and urea groups and soft segment (SS) parts formed mainly ofpolyol, which will lead to an improved moist heat resistance.

According to a preferred embodiment, after the addition of polyurethane,the resulting polyurethane-impregnated sheet-like article is dividedinto halves or a few parts in the sheet thickness direction, whichensures a high production efficiency.

Prior to the hair raising step described later, a lubricant such assilicone emulsion may be added to the polyurethane-impregnatedsheet-like article. According to another preferred embodiment, anantistatic agent is added prior to the hair raising step so that theground powder produced from the grinding of the sheet-like article ishindered from depositing on the sandpaper.

A hair raising step may be performed in order to raise hairs on thesurface of the sheet-like article. The hair raising treatment can beperformed by grinding with sandpaper, roll sander, or the like.

The thickness of the sheet-like article is preferably 0.1 to 5 mmbecause if the thickness is too small, physical characteristics such astensile strength and tear strength of the sheet-like article willdeteriorate whereas if the thickness is too large, the texture of thesheet-like article will become stiff.

The sheet-like article may be dyed. A preferable dyeing method is theuse of a jet dyeing machine which has a kneading effect to soften thesheet-like article while drying the sheet-like article. The polyurethanemay degrade if the dyeing temperature is too high whereas dyeing may notbe achieved completely if it is too low, and therefore, it may be setappropriately depending on the type of the fiber. In general, the dyeingtemperature is preferably 80° C. or more and 150° C. or less, morepreferably 110° C. or more and 130° C. or less.

The dye to be used should be selected to meet the type of the fiber thatconstitutes the fibrous base material. For example, a dispersed dye maybe used for a polyester-based fiber, and an acidic dye or ametal-containing dye may be used for a polyamide based fiber. Moreover,combinations of these dyes may also be employed. In the case where thesheet-like article is dyed with a dispersed dye, reduction cleaning maybe performed after the dyeing.

According to another preferred embodiment, a dyeing assistant may beused in the dyeing step. The use of a dyeing assistant can serve toimprove the dyeing uniformity and reproducibility. Furthermore,finishing with a softening agent, such as silicone, an antistatic agent,a water repellent, a flame retardant, a light resistance agent, anantimicrobial agent, etc. may be performed simultaneously with dyeing inthe same bath or sequentially by adding them after the dyeing step.

The sheet-like article obtained according to the present invention canbe suitably used mainly as artificial leather components of, forexample, the following: furniture, chairs and wall materials; interiormaterials with highly graceful external appearance for surfacedecoration of seats, ceilings, interiors, etc. of vehicles includingmotor vehicles, trains, and aircraft; shirts, jackets, and uppers,trims, etc. of casual shoes, sports shoes, men's shoes, women's shoes,etc.; bags, belts, wallets, etc., and clothing materials used as partsthereof; and industrial use materials such as wiping clothes, grindingclothes, and CD curtains.

EXAMPLES

Hereinafter, the sheet-like materials according to the present inventionand the method for production therefor are described in more detail withreference to Examples, although the present invention is not limitedonly to these Examples.

[Evaluation Methods]

(1) Falling-Off Rate of Polyurethane During Coagulation:

The mass of the fibrous base material alone and the mass of the fibrousbase material impregnated with a water-dispersed polyurethane dispersionliquid were measured, and the mass of solid polyurethane contained inthe material that corresponds to the difference between the measurementswas defined as polyurethane content A. Then, the aforementioned fibrousbase material impregnated with a water-dispersed polyurethane dispersionliquid was subjected to a coagulation step using hot water or steam anda subsequent drying step, followed by measuring the mass difference fromthe fibrous base material to give polyurethane content B. Thefalling-off rate of polyurethane during coagulation is expressed by thefollowing equation and the average of ten calculations made fordifferent measuring points was used for evaluation.

Falling-off rate of polyurethane (%)=polyurethane content B/polyurethanecontent A×100

(2) Measurement of Viscosity of Water-Dispersed Polyurethane DispersionLiquid:

A water-dispersed polyurethane dispersion liquid was prepared and itsviscosity was measured using a rotation viscometer (Brookfield typeviscometer manufactured by Tokyo Keiki Inc.) under the conditions of anambient temperature of 25° C. and rotating speeds of 0.5 rpm and 10 rpm.

(3) External Appearance Quality of Sheet-Like Article

The external appearance quality of a sheet-like article was rated on ascale of 1 to 5 based on visual inspection and sensory evaluation by atotal of 20 raters made up of 10 males and 10 females who were bothhealthy adults. The rating given by the greatest number of raters wastaken to represent the external appearance quality. For the externalappearance quality, specimens rated as grade 4 or grade 5 were assumedto be acceptable.

Grade 5: Uniformly raised hairs were found and the dispersed state offiber is good, resulting in a good external appearance.

Grade 4: This grade is between grade 5 and grade 4.

Grade 3: The dispersed state of fiber is partially not very good, butraised hairs were found, resulting in a fairly good external appearance.

Grade 2: This grade is between grade 3 and grade 1.

Grade 1: The dispersed state of fiber is very poor as a whole, and theexternal appearance is at rejectable level.

(4) Texture of Sheet-Like Article

The texture of a sheet-like article was rated on a scale of 1 to 3 basedon haptic sensory evaluation by a total of 20 raters made up of 10 malesand 10 females who were both healthy adults. The rating given by thegreatest number of raters was taken to represent the texture. Specimenshaving good texture (high in rubber elastic) were given the mark “⊚”.

⊚: Higher in flexibility and crease recoverability than artificialleather products produced from an organic solvent based polyurethane andhaving the same level of metsuke.

∘: Comparable in flexibility and crease recoverability to artificialleather products produced from an organic solvent based polyurethane andhaving the same level of metsuke.

x: The sheet is stiff and has a paper-like feel.

(5) Method for Calculating the Proportion Accounted for by NonporousPolymer Elastomer Masses Each with a Size of 50 μm² or More (ParameterA)

A specimen of artificial leather was cut either in the length directionor in the width direction and the thickness-directional cross section ofthe artificial leather was observed by scanning electron microscopy(SEM) at a magnification of ×500 to provide ten SEM images. An imageanalysis software program, namely, ImageJ (version 1.44p), developed bythe National Institutes of Health in the U.S. was used to calculate theproportion of those nonporous polymer elastomer masses each with a sizeof 50 μm² or more among all the polyurethane masses observed in thecross section to the total cross section of the artificial leathercontained in the field of view (4.3×10⁴ μm²) in each SEM image, followedby calculating the average over the ten images, which was used forevaluation. FIG. 3 is a schematic diagram showing the calculation methodfor parameter A. FIG. 3 is a schematic diagram showing a polyurethanemass, referred to as mass 1, for parameter A. Mass 1 of polyurethanerepresents a cross-sectional polyurethane region (those parts behind thecross section are not included) observed in the cross section of theartificial leather specimen.

(6) Method for Calculating the Polymer Elastomer Coverage on the CrossSection of Ultrafine Fibers (Parameter B):

A specimen of artificial leather was cut in the length direction or inthe width direction and the thickness-directional cross section of theartificial leather obtained was observed by scanning electron microscopy(SEM) at a magnification of ×500 to provide ten SEM images. An imageanalysis software program, namely, ImageJ (version 1.44p), developed bythe National Institutes of Health in the U.S. was used to select fiveultrafine fiber bundles that were observed to have been cutperpendicularly to the length direction of the fibers and calculate theproportion of the circumference of each ultrafine fiber bundle where itis in contact with resin film with a thickness of 1 μm or more. For thetotal of 50 observed ultrafine fibers (5×10 images), the average of thepolymer elastomer coverage on the cross section was calculated forevaluation. FIG. 4 is a schematic diagram showing the calculation methodfor parameter B. For parameter B, FIG. 4 gives a schematic diagram thatshows the circumference (circumference 2) of an ultrafine fiber and/orultrafine fiber bundle and the circumference (circumference 3) that iscovered by the polymer elastomer film. The solid line part illustratescircumference 2 of an ultrafine fiber bundle and the dotted line partshows circumference 3 that is covered by the polymer elastomer film.

[Preparation of Polyurethane Liquid A]

A polycarbonate diol with a Mn of 2,000 [Duranol (registered trademark)T5652, manufactured by Asahi Kasei Chemicals Corporation] used aspolyol, MDI as isocyanate, and 2,2-dimethylol propionic acid as theintramolecular hydrophilic group were reacted in a toluene solvent toprepare a prepolymer. Then, ethylene glycol and ethylene diamine used aschain extenders, polyoxyethylene nonylphenyl ether as externalemulsifier, and water were added and stirred, followed by removal oftoluene under reduced pressure to provide water-dispersed polyurethanedispersion liquid A.

[Preparation of Polyurethane Liquid B]

A polycarbonate diol with a Mn of 2,000 [Duranol (registered trademark)T6002, manufactured by Asahi Kasei Chemicals Corporation] used aspolyol, IPDI as isocyanate, and a diol compound with a polyethyleneglycol-containing side chain and 2,2-dimethylol propionic acid as theintramolecular hydrophilic groups were reacted in an acetone solvent toprepare a prepolymer. Then, ethylene glycol and ethylene diamine used aschain extenders, and water were added and stirred, followed by removalof acetone under reduced pressure to provide water-dispersedpolyurethane dispersion liquid B.

[Preparation of Polyurethane C]

A polycarbonate diol with a Mn of 2,000 [Duranol (registered trademark)T5652, manufactured by Asahi Kasei Chemicals Corporation] used aspolyol, IPDI as isocyanate, and trimethylolpropane as the intramolecularhydrophilic group were reacted in a methyl ethyl ketone solvent toprepare a prepolymer. Then, ethylene glycol and ethylene diamine used aschain extenders, polyoxyethylene nonylphenyl ether as externalemulsifier, and water were added and stirred, followed by removal ofmethyl ethyl ketone under reduced pressure to provide water-dispersedpolyurethane dispersion liquid D.

Example 1

Polyethylene terephthalate copolymerized with 8 mol % sodium5-sulfoisophthalate was used as sea component and polyethyleneterephthalate was used as island component to produce an island-in-seatype composite fiber in which the composition ratio was 20 mas % seacomponent and 80 mas % island component, the number of islands was 16islands/filament, and the average filament diameter was 20 μm. Theisland-in-sea type composite fiber obtained was cut into pieces with afiber length of 51 mm to provide staple. It was then passed through acard and a cross lapper to form a fiber web, which was subjected toneedle punching to produce a non-woven fabric.

The non-woven fabric obtained in this manner was shrunk by immersing itin hot water at a temperature of 97° C. for 2 minutes, and then dried ata temperature of 100° C. for 5 minutes. Subsequently, the resultingnonwoven fabric was impregnated with a dispersion liquid prepared byadjusting water-dispersed polyurethane dispersion liquid A to apolyurethane solid content of 20%, adding an association type viscosityimprover [Thickner 627N, manufactured by San Nopco Limited] to aneffective component content of 4 mass % relative to the polyurethanesolid content, and also adding magnesium sulfate to 1.2 mass % relativeto the polyurethane solid content. The fabric was then treated in hotwater at a temperature of 95° C. for 1 minute and air-dried in hot airat a drying temperature of 100° C. for 15 minutes, and the resultingsheet was heated additionally at a temperature of 160° C. for 20minutes. Thus, the resulting sheet consisted of a nonwoven fabric towhich water-dispersed polyurethane was added so that polyurethaneaccounted for 35 mass % relative to the mass of the island component.The falling-off rate of polyurethane during the polyurethane coagulationstep in hot water was as small as 0.1%, suggesting scarce occurrence.

Subsequently, the sheet thus obtained was immersed in an aqueous sodiumhydroxide solution with a concentration of 10 g/L heated at 95° C. andtreated for 25 minutes to remove the sea component from theisland-in-sea type composite fiber, thus providing a sea-free sheet. Thesingle fibers on the surface of the resulting sea-free sheet had anaverage single fiber diameter of 4.2 μm. Subsequently, the sea-freesheet was cut in half perpendicularly to the thickness direction using acutting-in-half machine with an endless band knife and the non-cutsurface was polished with 120-mesh and 240-mesh sandpapers to raisehairs. Then, it was dyed with a disperse dye using a circular dyeingmachine, followed by reduction cleaning to provide artificial leatherwith a metsuke of 221 g/m². The resulting artificial leather had goodappearance quality and good texture free of a paper-like feel. ParameterA was 4.0% and parameter B was 27.1%.

Example 2

Except that the same nonwoven fabric as in Example 1 was impregnatedwith a dispersion liquid prepared by adjusting water-dispersedpolyurethane dispersion liquid A to a solid content of 20%, adding anepoxy based crosslinking agent [CR-5L, manufactured by DIC] to aneffective component content of 5 mass % relative to the polyurethanesolid content, adding an association type viscosity improver [Thickner627N, manufactured by San Nopco Limited] to an effective componentcontent of 4 mass % relative to the polyurethane solid content, andadding magnesium sulfate to 1.2 mass % relative to the polyurethanesolid content, the same procedure as in Example 1 was carried out toprovide artificial leather with a metsuke of 223 g/m². The falling-offrate of polyurethane during the water-dispersed polyurethane coagulationstep in hot water was as small as 0.1%, suggesting scarce occurrence.The resulting artificial leather had good appearance quality and goodtexture free of a paper-like feel. Parameter A was 4.1% and parameter Bwas 25.4%.

Example 3

Polyethylene terephthalate copolymerized with 8 mol % sodium5-sulfoisophthalate was used as sea component and polyethyleneterephthalate was used as island component to produce an island-in-seatype composite fiber in which the composition ratio was 20 mas % seacomponent and 80 mas % island component, the number of islands was 16islands/filament, and the average filament diameter was 20 μm. Theisland-in-sea type composite fiber obtained was cut into pieces with afiber length of 51 mm to provide staple. It was then passed through acard and a cross lapper to form a fiber web, which was subjected toneedle punching to produce a non-woven fabric.

The non-woven fabric obtained in this manner was shrunk by immersing itin hot water at a temperature of 97° C. for 5 minutes, and then dried ata temperature of 100° C. for 10 minutes. Subsequently, an aqueoussolution containing 10 mass % (solid content) of PVA with a degree ofsaponification of 99% and a degree of polymerization of 1,400 [NM-14,manufactured by Nippon Synthetic Chemical Industry Co., Ltd.] was addedto the resulting nonwoven fabric, followed by drying at a temperature of100° C. for 10 minutes and additional heating at a temperature of 150°C. for 20 minutes to provide a sheet. Then, an aqueous sodium hydroxidesolution with a concentration of 100 g/L was heated at 50° C. and thesheet obtained above was immersed in it for 20 minutes to remove the seacomponent from the island-in-sea type composite fiber, thereby providinga sea-free sheet. The single fibers on the surface of the resultingsea-free sheet had an average fiber diameter of 4.2 μm. Following this,the sea-free sheet was impregnated with water-dispersed polyurethanedispersion liquid A prepared as in Example 2, treated in hot water at atemperature of 95° C. for 1 minute, and air-dried in hot air at a dryingtemperature of 100° C. for 15 minutes to provide a sheet containingwater-dispersed polyurethane in such a manner that polyurethaneaccounted for 35 mass % relative to the mass of the island component inthe nonwoven fabric. The aforementioned sheet containing water-dispersedpolyurethane was immersed in hot water at a temperature of 98° C. for 10minutes to remove the PVA added before, followed by drying at atemperature of 100° C. for 10 minutes. Subsequently, the resulting sheetwas further subjected to additional heating at a temperature of 160° C.for 20 minutes.

Then, the sea-free sheet was cut in half perpendicularly to thethickness direction using a cutting-in-half machine with an endless bandknife, and the non-cut surface was polished with 120-mesh and 240-meshsandpapers to raise hairs and dyed with a disperse dye using a circulardyeing machine, followed by reduction cleaning to provide artificialleather with a metsuke of 230 g/m². The falling-off rate of polyurethaneduring the water-dispersed polyurethane coagulation step in hot waterwas as small as 0.2%, suggesting scarce occurrence. The resultingartificial leather had good appearance quality and good texture free ofa paper-like feel. Parameter A was 3.8% and parameter B was 20.3%.

Example 4

Except that the same nonwoven fabric as in Example 1 was impregnatedwith a dispersion liquid prepared by adjusting water-dispersedpolyurethane dispersion liquid B to a solid content of 20% and adding anassociation type viscosity improver [Thickner 623N, manufactured by SanNopco Limited] to an effective component content of 3 mass % relative tothe polyurethane solid content, the same procedure as in Example 1 wascarried out to provide artificial leather with a metsuke of 218 g/m².

The falling-off rate of polyurethane during the water-dispersedpolyurethane coagulation step in hot water was as small as 0.1%,suggesting scarce occurrence. The resulting artificial leather had goodappearance quality and good texture free of a paper-like feel. ParameterA was 4.0% and parameter B was 26.8%.

Example 5

Except that the same nonwoven fabric as in Example 1 was impregnatedwith a dispersion liquid prepared by adjusting water-dispersedpolyurethane dispersion liquid B to a solid content of 20%, addingaqueous isocyanate [Desmodur (registered trademark) N3900, manufacturedby Bayer Material Science] to an effective component content of 3 mass %relative to the polyurethane solid content, adding carbodiimide basedcrosslinking agent [Carbodilite (registered trademark) V-02-L2,manufactured by Nisshinbo Chemical Inc.] to an effective componentcontent of 3 mass % relative to the polyurethane solid content, andadding an association type viscosity improver [Thickner 623N,manufactured by San Nopco Limited] to an effective component content of3 mass % relative to the polyurethane solid content, the same procedureas in Example 1 was carried out to provide artificial leather with ametsuke of 220 g/m².

The falling-off rate of polyurethane during the water-dispersedpolyurethane coagulation step in hot water was as small as 0.2%,suggesting scarce occurrence. The resulting artificial leather had goodappearance quality and good texture free of a paper-like feel. ParameterA was 4.3% and parameter B was 30.3%.

Example 6

Except that the same nonwoven fabric as in Example 3 was impregnatedwith a dispersion liquid prepared by adjusting water-dispersedpolyurethane dispersion liquid B to a solid content of 20%, addingaqueous isocyanate [Desmodur (registered trademark) N3900, manufacturedby Bayer Material Science] to an effective component content of 3 mass %relative to the polyurethane solid content, adding carbodiimide basedcrosslinking agent [Carbodilite (registered trademark) V-02-L2,manufactured by Nisshinbo Chemical Inc.] to an effective componentcontent of 3 mass % relative to the polyurethane solid content, andadding an association type viscosity improver [Thickner 623N,manufactured by San Nopco Limited] to an effective component content of3 mass % relative to the polyurethane solid content, the same procedureas in Example 3 was carried out to provide artificial leather with ametsuke of 220 g/m².

The falling-off rate of polyurethane during the water-dispersedpolyurethane coagulation step in hot water was as small as 0.2%,suggesting scarce occurrence. The resulting artificial leather had goodappearance quality and good texture free of a paper-like feel. ParameterA was 4.2% and parameter B was 20.4%.

Example 7

Except that the same island-in-sea composite fiber as in Example 1 waspassed through a card and a cross lapper to form fiber webs and theresulting webs were stacked, followed by sandwiching the stack of fiberwebs between two pieces of woven fabric with a weaving density of 96ends and 76 picks formed of 84-dtex, 72-filament twisted yarns used asboth warp and weft and processing the stack by needle punching toprovide complex nonwoven fabric; that water-dispersed polyurethane wasadded in such a manner that the mass of the polyurethane accounted for28 mass % relative to the mass of the island component of the nonwovenfabric; that the sea-free sheet was cut perpendicularly to the thicknessdirection using a cutting-in-half machine with an endless band knife;and that the exposed face was polished with 120-mesh and 240-meshsandpapers to raise hairs; the same procedure as in Example 6 wascarried out to produce artificial leather with a metsuke of 393 g/m².The falling-off rate of polyurethane during the water-dispersedpolyurethane coagulation step in hot water was as small as 0.2%,suggesting scarce occurrence. The resulting artificial leather had goodappearance quality and good texture free of a paper-like feel. ParameterA was 3.6% and parameter B was 20.1%.

Example 8

Except that the same nonwoven fabric as in Example 3 was impregnatedwith a dispersion liquid prepared by adjusting water-dispersedpolyurethane dispersion liquid A to a solid content of 20%, addingaqueous isocyanate [Desmodur (registered trademark) N3900, manufacturedby Bayer Material Science] to an effective component content of 3 mass %relative to the polyurethane solid content, adding a carbodiimide basedcrosslinking agent [Carbodilite (registered trademark) V-02-L2,manufactured by Nisshinbo Chemical Inc.] to an effective componentcontent of 3 mass % relative to the polyurethane solid content, adding apolysaccharide viscosity improver, namely, guar gum [Neosoft G,manufactured by Taiyo Kagaku Co., Ltd.], to an effective componentcontent of 2 mass % relative to the polyurethane solid content, andadding magnesium sulfate to 1.2 mass % relative to the polyurethanesolid content, and that hot water treatment was performed at atemperature of 95° C. for 3 minutes after the impregnation with apolyurethane dispersion liquid, the same procedure as in Example 3 wascarried out to provide artificial leather with a metsuke of 221 g/m².

The falling-off rate of polyurethane during the water-dispersedpolyurethane coagulation step in hot water was as small as 0.1%,suggesting scarce occurrence. It was also found that the face exposed bythe cutting with a cutting-in-half machine had little unevenness inpolyurethane distribution and the fibrous base material was impregnateduniformly with polyurethane. The resulting artificial leather had goodappearance quality and good texture free of a paper-like feel. ParameterA was 3.3% and parameter B was 18.9%.

Example 9

Except that the same island-in-sea composite fiber as in Example 1 waspassed through a card and a cross lapper to form fiber webs and theresulting webs were stacked, followed by sandwiching the stack of fiberwebs between two pieces of woven fabric with a weaving density of 96ends and 76 picks formed of 84-dtex, 72-filament twisted yarns used asboth warp and weft and processing the stack by needle punching toprovide complex nonwoven fabric; that water-dispersed polyurethane wasadded in such a manner that the mass of the polyurethane accounted for28 mass % relative to the mass of the island component of the nonwovenfabric; that the sea-free sheet was cut perpendicularly to the thicknessdirection using a cutting-in-half machine with an endless band knife;and that the exposed face was polished with 120-mesh and 240-meshsandpapers to raise hairs; the same procedure as in Example 8 wascarried out to produce artificial leather with a metsuke of 390 g/m².The falling-off rate of polyurethane during the water-dispersedpolyurethane coagulation step in hot water was as small as 0.1%,suggesting scarce occurrence. It was also found that the face exposed bythe cutting with a cutting-in-half machine had little unevenness inpolyurethane distribution and the fibrous base material was impregnateduniformly with polyurethane. The resulting artificial leather had goodappearance quality and good texture free of a paper-like feel. ParameterA was 2.9% and parameter B was 19.2%.

Example 10

Except for omitting the step of adding, to non-woven fabric, PVA with adegree of saponification of 99% and a degree of polymerization of 1,400[NM-14, manufactured by Nippon Synthetic Chemical Industry Co., Ltd.]and the step of drying, the same procedure as in Example 9 was carriedout to produce artificial leather with a metsuke of 388 g/m². Thefalling-off rate of polyurethane during the water-dispersed polyurethanecoagulation step in hot water was as small as 0.1%, suggesting scarceoccurrence. It was also found that the face exposed by the cutting witha cutting-in-half machine had little unevenness in polyurethanedistribution and the fibrous base material was impregnated uniformlywith polyurethane. The resulting artificial leather had good appearancequality and good texture free of a paper-like feel. Parameter A was 1.1%and parameter B was 4.9%.

Example 11

Except that nonwoven fabric was impregnated with a dispersion liquidprepared by adjusting water-dispersed polyurethane dispersion liquid Bto a solid content of 20%, adding aqueous isocyanate [Desmodur(registered trademark) N3900, manufactured by Bayer Material Science] toan effective component content of 4 mass % relative to the polyurethanesolid content, and adding a polysaccharide viscosity improver, namely,guar gum [Neosoft G, manufactured by Taiyo Kagaku Co., Ltd.], to aneffective component content of 2.5 mass % relative to the polyurethanesolid content, the same procedure as in Example 9 was carried out toprovide artificial leather with a metsuke of 388 g/m².

The falling-off rate of polyurethane during the water-dispersedpolyurethane coagulation step in hot water was as small as 0.1%,suggesting scarce occurrence. It was also found that the face exposed bythe cutting with a cutting-in-half machine had little unevenness inpolyurethane distribution and the fibrous base material was impregnateduniformly with polyurethane. The resulting artificial leather had goodappearance quality and good texture free of a paper-like feel. ParameterA was 2.5% and parameter B was 14.3%.

Example 12

Except that nonwoven fabric was impregnated with a dispersion liquidprepared by adjusting water-dispersed polyurethane dispersion liquid Cto a solid content of 20%, adding a carbodiimide based crosslinkingagent [Carbodilite (registered trademark) V-02-L2, manufactured byNisshinbo Chemical Inc.] to an effective component content of 4 mass %relative to the polyurethane solid content, adding a polysaccharideviscosity improver, namely, guar gum [Neosoft G, manufactured by TaiyoKagaku Co., Ltd.], to an effective component content of 2 mass %relative to the polyurethane solid content, and adding magnesium sulfateto 3.0 mass % relative to the polyurethane solid content, the sameprocedure as in Example 9 was carried out to provide artificial leatherwith a metsuke of 386 g/m².

The falling-off rate of polyurethane during the water-dispersedpolyurethane coagulation step in hot water was as small as 0.1%,suggesting scarce occurrence. It was also found that the face exposed bythe cutting with a cutting-in-half machine had little unevenness inpolyurethane distribution and the fibrous base material was impregnateduniformly with polyurethane. The resulting artificial leather had goodappearance quality and good texture free of a paper-like feel. ParameterA was 1.2% and parameter B was 5.2%.

Example 13

Except for omitting the step of adding PVA with a degree ofsaponification of 99% and a degree of polymerization of 1,400 [NM-14,manufactured by Nippon Synthetic Chemical Industry Co., Ltd.] and thestep of drying, the same procedure as in Example 12 was carried out toproduce artificial leather with a metsuke of 388 g/m². The falling-offrate of polyurethane during the water-dispersed polyurethane coagulationstep in hot water was as small as 0.1%, suggesting scarce occurrence. Itwas also found that the face exposed by the cutting with acutting-in-half machine had little unevenness in polyurethanedistribution and the fibrous base material was impregnated uniformlywith polyurethane. The resulting artificial leather had good appearancequality and good texture free of a paper-like feel. Parameter A was 0.7%and parameter B was 4.0%.

FIG. 1 is a cross section of the artificial leather sample prepared inExample 13. The observation of polyurethane masses and ultrafine fiberbundles given in FIG. 1 shows that the cross-sectional sizes of thepolyurethane masses are small (polyurethane masses are small) and alsothat the contact area between the ultrafine fiber bundles and thepolyurethane masses is small.

Comparative example 1

Except that the same nonwoven fabric as in Example 1 was impregnatedwith a dispersion liquid prepared by adjusting water-dispersedpolyurethane dispersion liquid A to a solid content of 20% and addingmagnesium sulfate to 1.2 mass % relative to the polyurethane solidcontent, the same procedure as in Example 1 was carried out to provideartificial leather with a metsuke of 223 g/m². The falling-off rate ofpolyurethane during the water-dispersed polyurethane coagulation step inhot water was 22.1%, suggesting the occurrence of uneven distribution ofpolyurethane added to the fibrous base material.

Comparative example 2

Except that the same nonwoven fabric as in Example 1 was impregnatedwith water-dispersed polyurethane dispersion liquid B adjusted to asolid content of 20%, the same procedure as in Example 1 was carried outto provide artificial leather with a metsuke of 223 g/m². Thefalling-off rate of the polyurethane during the polyurethane coagulationstep in hot water was 15.1%, suggesting the occurrence of unevendistribution of polyurethane added to the fibrous base material.

Comparative example 3

Except that the same nonwoven fabric as in Example 1 was impregnatedwith water-dispersed polyurethane dispersion liquid B adjusted to asolid content of 20%, treated for 5 minutes in a wet hot atmosphere at atemperature of 97° C. and a humidity of 100%, and dried for 15 minutesat a temperature of 110° C. in order for the addition of water-dispersedpolyurethane resin to lead the polyurethane to account for 35 mas %relative to the mass of the island component of the nonwoven fabric, thesame procedure as in Example 1 was carried out to provide artificialleather with a metsuke of 223 g/m². The falling-off rate of thepolyurethane during the water-dispersed polyurethane coagulation step inhot water was 0.0%, but the resulting artificial leather had a texturewith a significantly paper-like feel. Parameter A was 7.9% and parameterB was 42.2%.

Comparative example 4

Except that the same nonwoven fabric as in Example 13 was impregnatedwith water-dispersed polyurethane dispersion liquid B adjusted to asolid content of 20%, treated for 5 minutes in a wet hot atmosphere at atemperature of 97° C. and a humidity of 100%, and dried for 15 minutesat a temperature of 110° C. in order for the addition of water-dispersedpolyurethane resin to lead the polyurethane to account for 28 mas %relative to the mass of the island component of the nonwoven fabric, thesame procedure as in Example 13 was carried out to provide artificialleather with a metsuke of 389 g/m². The falling-off rate of thepolyurethane during the water-dispersed polyurethane coagulation step inhot water was 0.0%, but the resulting artificial leather had a texturewith a significantly paper-like feel. Parameter A was 8.1% and parameterB was 43.1%.

FIG. 2 is a cross section of the artificial leather sample prepared inComparative example 4. The observation of polyurethane masses andultrafine fiber bundles given in FIG. 2 shows that the cross-sectionalsizes of the polyurethane masses are large (polyurethane masses arelarge) and also that the contact area between the ultrafine fiberbundles and the polyurethane masses is large.

Results obtained in Examples 1 to 7 and Comparative examples 1 to 4 aresummarized in Tables 1 and 2.

TABLE 1 Water-dispersed polyurethane dispersion liquid ProcessabilityPoly- viscosity improver viscosity of viscosity of resin falling-urethane content coagulation prepared PU liquid prepared PU liquid offrate liquid type (mass %) method (mPa · s) 0.5 rpm (mPa · s) 10 rpm (%)Example 1 A Thickener 627N 4.0 hot water 650 653 0.1 Example 2 AThickener 627N 4.0 hot water 700 710 0.1 Example 3 A Thickener 627N 4.0hot water 700 710 0.2 Example 4 B Thickener 623N 3.0 hot water 800 8030.2 Example 5 B Thickener 623N 3.0 hot water 830 828 0.1 Example 6 BThickener 623N 3.0 hot water 830 828 0.2 Example 7 B Thickener 623N 3.0hot water 830 828 0.2 Example 8 A Neosoft G 2.0 hot water 2500 690 0.1Example 9 A Neosoft G 2.0 hot water 2500 690 0.1 Example 10 A Neosoft G2.0 hot water 2500 690 0.1 Example 11 B Neosoft G 2.5 hot water 2620 5400.1 Example 12 C Neosoft G 2.0 hot water 2300 682 0.1 Example 13 CNeosoft G 2.0 hot water 2300 682 0.1 Comparative A — — hot water 4.3 4.122.1 example 1 Comparative B — — hot water 5.1 5.2 15.1 example 2Comparative B — — moist heat 5.1 5.2 0.0 example 3 Comparative B — —moist heat 5.1 5.2 0.0 example 4

TABLE 2 Poly- Artificial leather urethane parameter parameter appearanceliquid A B texture quality Example 1 A 4.0 27.1 ◯ 3 Example 2 A 4.1 25.4◯ 4 Example 3 A 3.8 20.3 ⊚ 5 Example 4 B 4.0 26.8 ◯ 3 Example 5 B 4.330.3 ◯ 4 Example 6 B 4.2 20.4 ⊚ 5 Example 7 B 3.6 20.1 ⊚ 5 Example 8 A3.3 18.9 ⊚ 5 Example 9 A 2.9 19.2 ⊚ 5 Example 10 A 1.1 4.9 ⊚ 5 Example11 B 2.5 14.3 ⊚ 5 Example 12 C 1.2 5.2 ⊚ 5 Example 13 C 0.7 4.0 ⊚ 5Comparative A — — — — example 1 Comparative B — — — — example 2Comparative B 7.9 42.2 X 3 example 3 Comparative B 8.1 43.1 X 3 example4

The values of parameter A in Examples are smaller than those inComparative examples, suggesting that the polyurethane masses aresmaller and polyurethane is dispersed uniformly in the artificialleather to give a soft texture. The values of parameter B in Examplesare also smaller than those in Comparative examples, suggesting that thecontact area between the ultrafine fiber bundles and polyurethane massesis smaller to give a soft texture.

EXPLANATION OF NUMERALS

1: mass of polyurethane

2: circumference of an ultrafine fiber bundle

3: circumference covered by polymer elastomer film

What is claimed:
 1. A production method for a sheet-like article, comprising a step for adding an aqueous resin dispersion liquid containing a water-dispersed polymer elastomer and a viscosity improver to a fibrous base material and a step for coagulating the polymer elastomer in hot water at a temperature of 50° C. to 100° C., wherein the sheet-like article comprising a fibrous base material formed of ultrafine fibers and/or ultrafine fiber bundles provided with, as a binder, a polymer elastomer having a hydrophilic group, any thickness-directional cross section of the sheet-like article containing regions occupied by the polymer elastomer, the regions including independent regions each with a cross-sectional area of 50 μm² or more, the total area of the independent regions accounting for 0.1% or more and 5.0% or less of the cross-sectional area of the sheet-like article in an observation view field.
 2. A production method for a sheet-like article as claimed in claim 1, wherein the aqueous resin dispersion liquid has non-Newtonian properties.
 3. A production method for a sheet-like article as claimed in claim 1, wherein the viscosity improver is a nonionic viscosity improver.
 4. A production method for a sheet-like article as claimed in claim 1, wherein the aqueous resin dispersion liquid has thixotropic properties.
 5. A production method for a sheet-like article as claimed in claim 1, wherein the viscosity improver is a polysaccharide viscosity improver.
 6. A production method for a sheet-like article as claimed in claim 1, wherein the viscosity improver is guar gum.
 7. A production method for a sheet-like article as claimed in claim 1, wherein the aqueous resin dispersion liquid contains a thermosensitive coagulant.
 8. A production method for a sheet-like article as claimed in claim 1, wherein the aqueous resin dispersion liquid contains a crosslinking agent.
 9. A production method for a sheet-like article as claimed in claim 1, wherein the polymer elastomer is water-dispersed polyurethane. 